As a conventional cutting insert for threading, there is the one as shown in Patent Literature 1. The cutting insert for threading of Patent Literature 1 has a square block shape and has two opposing end surfaces, three side surfaces which form right angles with these end surfaces, and a saw-tooth-like side surface. An even number of protruding portions of the saw-tooth-like side surface each have a shape corresponding to a thread groove and define a cutting edge for threading. The protruding portion of the saw-tooth-like side surface has a shape extending over between the two end surfaces, and the protruding portions include two protruding portions which define a cutting edge on one end surface and two protruding portions which define a cutting edge on the other end surface. In this cutting insert, both of the end surfaces can be used as surfaces with the cutting edges for threading in this way.
This cutting insert of Patent Literature 1 is attached to a tool body via a shim plate and a cartridge and thereby a cutting edge for machining a thread groove is given to the cutting tool for threading. The cutting insert has two through holes and each through hole extends so as to be orthogonal to the two end surfaces. According to description in Patent Literature 1, this cutting insert is clamped by a clamp member which engages with these through holes.